Scale-dependent movements and protection of female blue crabs (Callinectes sapidus)

Abstract

Little is known about the migration of female crabs (Callinectes sapidus) to spawning grounds, or how effectively they are protected by North Carolina's “spawning sanctuaries.” To investigate migration, we tagged and released a total of 2700 mature female crabs in the fall of 2001 and the summer and fall of 2002 in the three tributaries of Pamlico Sound. Tag returns indicate that females begin migration during September to November and that they probably do not complete it until the next spring. To assess site fidelity and protection of females by spawning sanctuaries, 398 tagged adult females were released in or near sanctuaries at Ocracoke and Hatteras inlets. Most recaptures occurred near the barrier islands (Outer Banks), suggesting that mobility declines once females reach euhaline waters, but recapture data also showed that crabs move over scales larger than sanctuaries and derive only temporary protection by entering sanctuaries. Ovigerous females fitted with ultrasonic pingers were tracked after release inside the boundary of Ocracoke spawning sanctuary. Crabs with orange (new) egg masses meandered over small areas, but those with eggs approaching hatching moved directly seaward. Apparently spawning sanctuaries must be large to be effective; where this is not practical (as in North Carolina), other strategies should be considered.